1. Field of the Invention
The present invention relates to a pressure detecting apparatus which detects the peak of combustion pressure in a cylinder of an internal combustion engine and the timing of the peak.
2. Description of the Prior Art
FIG. 1 is a schematic view showing a conventional apparatus for detecting pressure in a cylinder. In the figure, numeral 20 denotes a pressure sensor which is mounted to an internal combustion engine (not shown in the drawings) and senses the combustion pressure in the cylinder, while numeral 21 denotes a conventional detecting device which detects the peak of combustion pressure in the cylinder and the timing of the peak. The waveform of combustion pressure in the cylinder detected by the pressure sensor 20 is inputted into the detective device 21, which detects the peak of the waveform (P.sub.max) and the timing of the peak (.theta..sub.pmax).
FIG. 2 shows graphs designating the size-relationship between the peak of combustion pressure (P.sub.1 in the figure) and the motoring P.sub.max (P.sub.2 in the figure), wherein the vertical line and the horizontal line denote pressures and crank angles respectively. Also in the figure, the point A on the horizontal line indicates the moment when the piston of the internal combustion engine has reached Top Dead Center (TDC). FIG. 2(a) shows the pressure waveform in the case where the peak of combustion pressure is greater than the motoring P.sub.max, while FIG. 2(b) shows that in the case where the former is equal to or less than the latter.
When that relationship is represented by such a waveform as shown in FIG. 2(a), the peak of combustion pressure can be detected easily by means of the conventional apparatus because the peak of combustion pressure is greater than the motoring P.sub.max. To the contrary, when the relationship is represented by such a waveform as shown in FIG. 2(b), that is, when the peak of combustion pressure is less than the motoring P.sub.max, particularly in the case where the pressure waveform lacks the maximum value, there has been a trouble that it has been very difficult for the conventional apparatus to detect the peak of combustion pressure and the timing of the peak.